Given the ever-increasing capacity demands made on communications networks, network designers have employed higher symbol rates. However, as operating symbol rates increase, deteriorating effects such as fiber nonlinearities and polarization mode dispersion inhibit communications over optical fiber. Accordingly, modulation formats exhibiting high spectral efficiencies have been employed in an attempt to mitigate such deteriorating effects. Notwithstanding improvements afforded by such efficient formats, methods and apparatus that provide an increased energy efficiency would represent a significant advance in the art.